Abstract: The paper introduces a new solution to the problem of communication between host and IC card read-write device using RS232 interface by way of using USB interface instead. The process how to read and write data through IC card using the I²C bus protocol and the communication process between the USB interface chip PDIUSBD12 and PC host are described. The USB architecture of firmware and the way to develop the function driving program is explained. The IC card read-write device uses USB interface to communicate with host and supports the function of plug and play, thus improving obviously the data transmission rate and ensuring the reliability and portability of the system. The device has been developed and put into applications successfully with its practicability proved.